1. Field of the Invention
The present invention relates to aqueous, pigment-based ink compositions for use in ink jet printers. These compositions comprise an insoluble pigment, a polymer that contains a bound nonionic aliphatic surfactant, and a carrier medium. The ink compositions are characterized by water and accent marker resistance properties, while achieving excellent print quality, jetting properties, storage stability, reliability, and drying times.
2. Description of Related Art (Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98)
Prints made from commercial aqueous, pigment-based, ink jet inks exhibit poor resistance to water and accent markers and are lower in optical density than prints made from laser printers. Those skilled in the art seek to eliminate these deficiencies. A suitable ink jet ink additive has been sought which would allow the ink jet printer producers to achieve optical densities now achieved only by laser printer producers, while imparting excellent resistance to water and accent markers.
Ink jet printing involves placement, in response to a digital signal, of small drops of a fluid ink onto a surface to form an image without physical contact between the printing device and the surface. In drop-on-demand (DOD) ink jet printing systems, liquid ink droplets are propelled from a nozzle by heat (thermal or bubble ink jet) or by a pressure wave (piezo ink jet). Thermal or bubble ink jet inks typically are based on water and glycols. Piezo ink jet systems generally use aqueous, solvent, or solid inks. These last inks, also known as phase change inks, are solid at ambient temperature and are liquid at printing temperatures.
The following properties are required of an ink composition for ink jet printing:
(a) high quality printing (edge acuity and optical density) of text and graphics on substrates, in particular, on uncoated cellulosic paper; PA1 (b) short dry time of the ink on a substrate such that the resulting printed image is not smudged when rubbed or offset onto a subsequent printed image placed upon the print; PA1 (c) good jetting properties exhibited by a lack of deviation of ink droplets from the flight path (misplaced dots) and of ink starvation during conditions of high ink demand (missing dots); PA1 (d) resistance of the ink after drying on a substrate to water and to accent markers; PA1 (e) long-term storage stability (no crust formation or pigment settling); and PA1 (f) long-term reliability (no corrosion, nozzle clogging, or kogation). PA1 (i) at least 0.1% by weight based on the total weight of the polymer of a monomer represented by the following formula: ##STR1## where: R.sub.1 is H, CH.sub.3, or C.sub.6 H.sub.5 ; PA1 (ii) at least one ethylenically-unsaturated monomer selected from the group consisting of olefins, mono vinylidene aromatics, alpha beta ethylenically-unsaturated carboxylic acids and esters thereof, ethylenically-unsaturated dicarboxylic anhydrides, and mixtures thereof.
Inks are known that possess one or more of the above listed properties. However, few inks are known that possess all of the above listed properties. Often, the inclusion of an ink component meant to satisfy one of the above requirements can prevent another requirement from being met. For example, the inclusion of a polymer in the ink composition can improve the water and accent marker resistance of the ink on a substrate after drying. However, the polymer can cause flocculation or settling of the pigments and impair jetting properties and long-term storage stability. Thus, most commercial ink jet inks represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed requirements.
Attempts made to meet the desirable ink jet ink criteria listed above are disclosed in U.S. Pat. Nos. 5,565,022; 4,384,096; 4,138,381; 4,077,926; 3,894,980; 3,891,591; 3,657,175. The inks of these patent disclosures, however, do not teach accomplishment of resistance to water and accent markers and increased optical density while continuing to achieve other desirable ink jet ink properties.
Accordingly, an object of the present invention is to provide improved pigment-based ink compositions capable of satisfying simultaneously the properties required of an ink composition for ink jet printing, especially the aforementioned properties (a) to (f).
Another object of the instant invention is directed to preparation of a polymer that provides an ink composition for ink jet printing with reduced water and accent marker sensitivity.
Still another advantageous feature of the invention which is the subject matter of this application is to provide an ink that has excellent filterability such that the ink can be filtered during manufacturing without ruining the filters. Other objects and advantages of the present invention will become apparent from the following disclosure.